Hiding power may be defined as a coating's ability to visibly obscure a surface onto which it is applied. Most coating manufacturers try to create coatings, such as paints, having high hiding power. Unfortunately, many challenges can occur during coating manufacturing resulting in final coatings having low hiding power. Combining coating components with insufficient attention to composition and interaction between components may result in uncontrolled flocculation, grit, or in the extreme case, gelation during its manufacturing, while it is sitting on a shelf, or upon its drying. Agglomeration of coating components, a cause of grit formation and gelation, as well as heterogeneous spacing of components in the final film are therefore undesirable as these factors lead to reduced hiding power of the coating. A need exists to control component spacing to help organize components, such as inorganic particles, to avoid agglomeration and maximize a coating's hiding power by creating an organized structure of composition components.
Some technologies counteract these problems by adding specific components to the paint that solely function to increase hiding power. One mechanism involves the delivery of air voids within a coating composition. These air voids may be delivered as individual particles (U.S. Pat. No. 4,427,836) or as part of a structure that encapsulate TiO2 particles (US20100048750). The size of the voids contributes to the organization of coating particles and enhances total hiding power based on the cumulative effect of Mie scattering and reduction of the apparent refractive index of the coating. Enhanced hiding results from the delivery of air to the coating and is not due to specific binding interactions between pigment and other paint components.
Additional methods to maximize hiding power and keep components separated in a composition include the addition of bulky organic/inorganic coatings on the surface of inorganic particles. Other methods modify the surface of inorganic particles with functional spacers to create steric hindrance or electrostatic repulsion between components of a composition. Some methods enhance the hiding power of a coating by adding additional components such as micron-sized inorganic host particles that physically bind pigment particles in well-spaced pores (US2013029880).
The hiding power of a coating can also be increased by the addition of functionalized latex solid particles to a coating. The solid latex particles bind covalently (U.S. Pat. No. 7,179,531) or non-covalently (US2013/0096250) to inorganic particles in a coating to aid in particle spacing and organization. Problems with this technology include the formation of strong, uncontrolled associations or attachments between the functionalized latex solid particles and inorganic particles that leads to grit formation, less than optimal hiding power, and reduced gloss and scrub resistance of resultant coatings. Variations in functional particle composition, the ratio of functional particles to inorganic particles, order of addition, and mixing intensity have been attempted to reduce adverse effects of uncontrolled strong binding (U.S. Pat. No. 6,576,051 and EP2426166).
Weaker non-covalent associative bonds formed between components of a composition may enhance hiding power of a coating by spacing the components under conditions that reduce grit formation. However, problems exist with forming bonds between components when there are pH changes within a coating as it dries, adsorbing dispersants, thickeners, binders, and increased mixing intensity in an aqueous dispersion as a coating is being manufactured. What is desired is a method of enhancing the hiding power of a coating that allows components of a coating to form stronger bonds, such as covalent bonds, without increasing the likelihood of grit formation or the need for extensive process control during formulation and the final drying of a coating, such as paint.